In 1980, the U.S. Environmental Protection Agency concluded that waste water from creosote and PCP wood-preserving processes poses an immediate or potential hazard to human health and the environment when improperly treated, stored, or disposed of. Moreover, pond sediments and sludges contaminated with wood preservatives were considered hazardous. Such materials are categorized as K001 hazardous wastes (49 CFR ch.1 subpart 172.101).
Creosote contamination is generally associated with surface soils, waters in treatment lagoons or evaporation areas, and groundwater contaminated with leachate from the above sources. There are approximately 550 sources of such waste in the United States where wood preserving is currently conducted (Micklewright, J. T. [1986] Contract report to the American Wood-Preserver's Institute. International Statistics Council, Inc., Washington, D.C.). Collectively, active treatment facilities generate an estimated 840 to 1530 dry metric tons of K001 sludge annually (Sikora, L. J. [1983] In Land Treatment of Hazardous Wastes, Parr, J. G., P. B. Marsh, eds.; Noyes Data Corp., Park Ridge, N.J., pp. 397-410). Although the number of operating wood-preserving facilities has been reduced, it has been estimated that there are 700 sites throughout the United States where wood preservation is, or has been, conducted (Burton, M. B., M. M. Martinson, K. D. Barr [1988] Biotech USA. 5th Ann. Indust. Conf., Nov. 14-16, San Francisco, CA). Since creosote treatment sites are commonly impacted by leaking tanks, drippings from treated lumber, spills, and leachate from unlined holding ponds, this number presumably describes the number of creosote-contaminated sites as well.
A major concern when discussing creosote contamination focuses on persistence of toxic constituents. Under appropriate conditions, all creosote constituents are potentially degradable. Therefore, persistence tends to be a function of impregnation within the wood as opposed to an inherent recalcitrance. For example, Petrowicz and Becker (Petrowicz, H. J. and G. Beckare [1964] Materialprufung 6:461-570) demonstrated that creosote constituents were recovered from creosote-treated wooden blocks; 16 of these compounds were identified as naphthalene, 2-methylnaphthalene, biphenyl, dimethylnaphthalene, acenaphthene, dibenzofuran, fluorene, methylfluorene, (anthracene and phenanthrene), carbazole, methylphenanthrene, 2-phenylnaphthalene, fluoranthene, pyrene, 2,3-benzo[b]fluorene, and chrysene. The same chemicals were recovered from unweathered blocks.
Becker and Petrowicz (Becker, G. and H. J. Petrowicz [1965] Materialprufung 7:325-330) showed that more than 30 years after initial application, creosote-treated railroad ties exhibited only a minor change in creosote composition. Rotard and Mailahn (Rotard, W. and W. Mailahn [1987] Anal. Chem. 59:65-69) employed more refined analytical techniques and found a significant amount of creosote present in discarded railroad crossties that had been installed in playgrounds. The most common constituents identified were (in order of decreasing concentration) phenanthrene, anthracene, fluoranthene, pyrene, chrysene, benzo[a]pyrene, benzo[b]fluoranthene, and benzo[j]fluoranthene.
Coal-tar creosote has been widely used as a wood preservative for over 150 years with an anual consumption in 1986 estimated at 454,000 metric tons (Mattraw, H. C. Jr., and B. J. Franks [1986] Chapter A. "Description of hazardous waste research at a creosote works, Pensacola, FL," pp. 1-8. In A. C. Mattraw, Jr., and B. J. Franks [eds.], USGS survey of toxic wastes-groundwater contamination program. USGS Water Supply Paper No. 2285). Though creosote-treated products themselves do not appear to represent a threat to the environment, accidental spillage and improper disposal of creosote at production plants and at wood-preserving facilities have resulted in extensive contamination of soil, surface water, and groundwater aquifers (Fisher, C. W., and G. R. Tallon [1971] Proceed. Am. Wood-Preservers' Assoc. 67:92-96; Goerlitz, D. F., D. E. Troutman, E. M. Godsy, and B. J. Franks [1986] Chapter G, pp. 49-53. USGS Water Supply Paper No. 2285). Since creosote contains many toxic compounds and priority pollutants, such sites are considered hazardous; hence, remedial action is required.
Recent studies have suggested that biodegradation may represent a clean and efficient means of remediating such sites. It has also been reported that 85% of creosote consists of polycyclic hydrocarbons (PAH's). Therefore, biodegradation of these constituents would result in the removal of a significant volume of creosote pollutants. Moreover, the destruction of these components would significantly reduce the potential health hazards associated wtih creosote-contaminated environments. Likewise, other environments similarly affected by PAH's (i.e., oil refineries, coal gasification sites) may also be improved significantly by removing the hazards associated with this class of chemical pollutant.
Microorganisms capable of degrading certain creosote PAH's have been described, and mechanisms for PAH biodegradation have been reviewed (Cerniglia, C. E., and S. K. Yang [1984] Appl. Environ. Microbiol. 47:119-124). Microbial degradation of lower molecular weight PAH's such as naphthalene and biphenyl by a variety of bacterial strains is well established. Biodegradation of tricyclic compounds such as anthracene and phenanthrene has also been reported.
There appear to be no accounts of the microbial utilization of PAH's containing four or more aromatic rings. However, several publications have described the co-metabolism of such PAH's including benzo[a]anthracene, benzo[a]pyrene, fluoranthene, and pyrene. Incidental metabolism of various PAH's by the ligninolytic fungus Phanerochaete chrysosporium grown under defined conditions has also been reported.
The basic principle of bioremediation is to exploit the ability of microorganisms to catabolize a wide range of organic substrates. Trickling filtration, land-farming, activated sludge, oxidation lagoons, and soil inoculation represent a few means in which microorganisms are utilized to treat industrial wastes in situ. For bioreactor operations, engineering designs are based on the unique demands of a particular microbial consortium or pure culture so as to provide the ideal environment, thereby optimizing the process. When successful, bioremediation results in the conversion of a toxic chemical to non-toxic materials.
Though there has been a large amount of research concerning the remediation of creosote-contaminated sites, there remains a need for more effective biological systems to accomplish this goal. The invention, described and claimed herein, is directed to the use of novel microbes which can be used to remediate creosote-contaminated sites.